Mimosa Trees??

[MasterPlumbersKeymaster]

I have a mimosa tree growing just at the end of my septic drain field. The tree is not huge, maybe 12′ tall, with several trunks, all no more than 4″ in diameter. I have been told by a few people that the mimosa will cause damage to the field because it has such an extensive, vigorous root system. Is this true?? I’d like to know before I kill a pretty tree.

[John Aldrich1Participant]

Onna, damage to septic systems, and sewer pipelines does occur from tree root intrusion quite commonly. Roots from just about all species of trees tend to grow through the joints in sewer pipelines, into cracks, and seams in septic tanks, and even up into the plumbing system of homes. The roots grow toward the water, and other nutrients contained in the sewage. Ultimately the roots become so dense in some instances that they clog the sewer pipes, or fill the septic tank. This condition causes the sewage to back-up into the house. That is the bad news.

However, my belief is that the STRATEGIC, and PROPER location of trees around a soil absorption system is beneficial to the performance of the system by utilizing the nutrients for growing the trees, and removing the water through evapotranspiration.

A case in point is a particular system that I have seen where a very large willow tree is thriving at the far end of a bed type soil absorption system. The tree was planted approximately 20 years ago. This vigorous, water loving tree has attained a height of about 40 feet, with a trunk DBH (Diameter Breast High) of 36 inches. The roots have extended into the gravel of the leach field but have not grown into the distribution pipes. The roots get all of the water that they need without growing into the pipes.

I estimate that this tree utilizes, and evaporates 200 to 300 gallons of water per day in the summer, and perhaps half of this volume in the winter. The tree also utilizes the nitrogen, and phosphorus that is in the septic tank effluent thereby reducing the application of these nutrients to the groundwater.

Another case in point is the leach field that serves my home, which is located approximately 6 feet from the base of a very large Siberian Elm tree, and is functioning very well. My leach field consists of a gravelless leach field material called SB*2. The SB*2 is a large diameter corrugated plastic pipe with a geotextile covering. The geotextile is intended to prevent soil siltation, and prevent root intrusion into the pipe. I installed this system 20 years ago and have observed no evidence of root intrusion from this Elm tree. The leach field has monitoring and ventilation ports on each end of each separate trench so that visual inspection of the inside of the tubing can be accomplished.

If your Mimosa tree is indeed located at the end of leach field, I suspect that it will perform in the same manner. Avoid planting trees close to the septic tank, or near the sewage pipe leading to it. JWA

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